1. Field of the Invention
This invention is generally directed to timing mechanisms for advancing or retarding the closing of an intake valve into the combustion chamber or cylinder of an internal combustion engine so as to regulate the power developed within the cylinder in proportion to the demand on the engine which demand is controlled by the throttle associated with the engine. More specifically, the present invention is directed to a mechanism for altering the period of closing of the intake valve of an internal combustion engine utilizing a split cam having a first lobe for controlling the opening of the intake valve and second lobe for controlling the closing of the intake valve. The second lobe may be angularly advanced or retarded with respect to the first lobe so as to selectively adjust the duration of opening of the intake valve. With the structure of the present invention the first lobe of the split cam is driven in direct relationship to the rotation of the engine's crankshaft by being fixed to a primary cam shaft. A secondary parallel cam shaft is also provided which is drivingly connected to the primary cam shaft but which is shiftable, or includes segments which are shiftable, relative to the primary cam shaft. A floating drive gear is mounted to the auxiliary cam shaft and engages a gear associated with the second lobe of the split cam in such a manner that, as the auxiliary cam shaft is axially shifted, the second lobe of the split cam will be angularly adjusted relative to the first lobe to thereby alter the duration of opening of the intake valve.
1. History of the Related Art
In internal combustion engines the amount of power developed by the engine and the fuel efficiency of the engine can be controlled by the timing of the intake and exhaust valves. There have been many inventions directed to altering the timing of intake and exhaust valves associated with internal combustion engines by adjusting the drive relationship between the engine's crankshaft which is driven by the pistons and the cam shaft on which cams are mounted for controlling the opening and closing of the valves by way of valve lifters or valve stems.
As engine efficiencies can be increased if the intake and exhaust valves are varied in direct relationship to the engine speed there have been numerous inventions also directed to altering the effective time of compression of a fuel change or in direct response to the engine throttle controls or to the speed of the engine's crankshaft. By varying either the positioning of a cam relative to a cam shaft or by utilizing variable nose cams to increase the effective operable width of the cam during its rotation, variations in the valve opening duration can be achieved.
By controlling the duration that an intake valve is open, the effective power developed by the engine during each piston stroke may be selectively altered. For example, when minimum power is required, if the intake valve is left open after the beginning of the compression stroke of a piston within a cylinder, a portion of the introduced air-fuel mixture will be forced back out through the intake valve and only a portion of the original mixture will be compressed after the valve is closed. However to obtain maximum engine power, the intake valve is closed as the piston reaches it bottom dead center (BDC) position so that the air-fuel mixture will be compressed during the entire compression stroke. In view of the foregoing, engine efficiency is directly related to properly controlling the timing of the opening and closing related to the fuel intake valves.
In U.S. Pat. No. 1,632,223 to Fey, an earlier type of cam control mechanism is disclosed wherein the angular position of the cams relative to the cam shaft may be selectively altered so as to advance or retard the opening and closing of the engine's intake and exhaust valves. Unfortunately, with such an arrangement the duration of opening of intake valves may not be selectively adjusted. Such a mechanism only functions to either advance or retard the timing of the opening but not the duration of the opening and thus does not effectively adjust for optimum fuel efficiency and engine power by controlling the duration of opening of the fuel intake valves or the "dwell" of the valves.
In U.S. Pat. No. 4,917,058 to Nelson et al., a mechanism for controlling the dwell time of either an intake or discharge valve of an internal combustion engine is disclosed. The mechanism includes an outer cam shaft and an inner cam shaft and a split cam having a fix lobe mounted to one of the inner or outer shafts and a selectively adjustable lobe secured to the other of the inner or the outer shafts. By controlling the rotation of the inner and outer shafts relative to one another the dwell or time of opening of either an intake or exhaust valve may be selectively controlled.
In U.S. Pat. No. 4,522,085 to Kane, another type of variable lobe cam mechanism for controlling the duration of opening of an intake valve for an internal combustion engine is disclosed. This invention also utilizes a split cam arrangement for altering the profile of the cam that acts upon a follower or other mechanism for controlling the opening of an intake valve. The cam shaft includes oppositely directed spiral grooves to which each lobe of the split cam are respectively engaged so that as the shaft is shifted axially the angular relationship between the two lobes is directly varied thereby either increasing or decreasing the amount of cam contact surface which controls the timing of the opening of the intake valve. The movement of the cam shaft is controlled by weights which are thrown outwardly by centrifugal force at increased engine speeds thereby shifting the shaft and causing the phase angle change between the split lobes of the intake control cam. Appropriate springs are provided to return the cam to its original lobe configuration as engine speed is reduced. Other patents directed to inventions utilizing cam lobe pairs which act in concert to create a variation in cam lobe dimension are disclosed in U.S. Pat. No. 1,175,395 to Wxion, French Patent 1,109,790 and German Patent 2,921,645. In both the French and German Patents both lobes of the cams are shiftable either by engagement with a concentrically splined shaft or with a sliding rod whereas in the Wxion Patent only one of the lobes of the cams is rotatable relative to the cam shaft.
Other examples of intake valve control cam devices are disclosed in U.S. Pat. Nos. 1,787,717 to Boulet, 2,967,519 to Rossger and 5,090,366 to Gondek.